I just finished assembling a 6" pier for my Schaefer mount. The pier is made up from 1-1/4" aluminum angle, 6"x36"x5/16" wall alum tubing, 3/8 SS turn buckles, 3/16 steel pop rivets, and 2 specially machined 3/4" alum plates.
The crutch legs are made from 4 pieces of alum angle fastened with steel pop rivets. These seem strong enough as is, but I will have them spot welded before painting. The advantage of this design is saving the welder time of assembly and me $$$. The key to this pier is the machined plate where the upper legs are fastened. It is a triangular piece with a 6" hole bored in the center and three 6" bosses machined 120* apart.
This is the classic Schaefer design and now has been used in many portable piers.
The mount is being powder coated now, so I will post a shot of the completed mount later. lynn